The invention discloses a high-flame-retardance polyisocyanurate hard foam easy for industrialized production and a preparation method thereof. The high-flame-retardance polyisocyanurate hard foam is prepared from a white material and polyisocyanates according to a mass ratio of 1:1.2-1:1.8 at 10-30 DEG C by utilizing a polyurethane low-pressure foaming machine, wherein the white material employs at least one kind of polyester polyol, at least one kind of liquid fire retardants and a solid fire retardant coated with red phosphorus capable of being conveniently dispersed in the liquid raw material. The high-flame-retardance polyisocyanurate hard foam provided by the invention has excellent flame retardance with the oxygen index larger than 30, and also has good dimension stability and thermal insulation performance while with a relatively low density.